From Wiktionary, the free dictionary
From ב־ (b'-, “in”) + ערום (arúm, “naked”).
בֶּעָרוּם • (be'arúm)
- naked, nude, in the nude
- While used much as an adjective, בערום is grammatically a prepositional phrase, and therefore does not inflect for gender, number, or definiteness.